1. Field of the Invention
The present invention relates generally to a mobile communication Base Station (BS) system, and in particular, to a Voice over Internet Protocol (VoIP) downlink packet scheduling apparatus and method.
2. Description of the Related Art
Recently, Voice over Internet Protocol (VoIP) service, which has been applied mostly to wired networks, has been adapted to wireless networks. The wireless networks are subject to expensive radio channels and low throughput, as compared to wired networks. Accordingly, it is advantageous to utilize the radio channel at maximum efficiency.
VoIP service requires real-time Quality of Service (QoS) which is not sensitive to losses, but very sensitive to packet delay time. VoIP service can retain the QoS of a user in the event of packet loss below a certain rate. Hence, it is important for the VoIP service to deliver the packet to a corresponding Mobile Station (MS) in time at the cost of packet loss.
A conventional mobile communication Base Station (BS) system fundamentally carries all of the received VoIP packets. Thus, the conventional mobile communication BS system has to deliver the VoIP packet even if the VoIP packet may be delayed in the system due to instantaneous throughput degradation based on the characteristic of the radio channel. In case where the packet is not transmitted but buffered to a system buffer, the packet is stored up to the buffer upper-bound capacity and the following VoIP packet is dropped. Hence, the delayed packet adversely affects the following packet.
Generally, when transmitting the VoIP packet over the wireless network, the conventional system may request oversubscription above a link capacity using a statistical multiplex scheme so as to efficiently utilize the limited radio resources. In doing so, the VoIP traffic over the link capacity may be loaded at a certain time. Consequently, the conventional system is subject to a frequent instantaneous bottleneck within the BS.